Pens used with printing devices are described in numerous publications, including U.S. Pat. No. 4,500,895 to Buck et al. The Buck patent describes a printing apparatus having a thermal-type ink-jet print head in communication with an ink reservoir. The print head is controlled for selectively ejecting ink drops to paper to form an image or characters.
An ink-jet type print head may include an outer layer that is designated an orifice plate. The orifice plate includes nozzles or orifices formed through it and is attached to the base of the print head. Ink is delivered from a reservoir in the body of the pen through channels formed in the print head to connect with each orifice. Drops of ink are ejected through the orifices toward the adjacent paper or other printing medium.
Mechanisms for controlled ejection of ink drops through an orifice may include a thin-film resistor, which is carried on the print head base adjacent to the orifice. Whenever a drop of ink is to be ejected from the orifice, a current pulse is directed to the resistor to ohmically heat the resistor and to vaporize a portion of the ink next to the resistor. The resultant expansion of the ink portion forces a minute ink drop through the orifice toward the paper.
In the past, the orifice plate and base components of a print head were attached by adhesives that were thermally cured. The use of thermally cured adhesives requires "tacking" the components together, employing, for example, other adhesives, prior to the application of the thermal-cure adhesive. Alternatively, the components are placed in a fixture during adhesive curing. These conventional approaches require several process steps, thereby increasing manufacturing complexity and time and the risk of component-to-component misalignment.
Adhesives may fail in harsh environments, such as is found in printing devices. Causes for such failures are many, including the forces attributable to the thermal expansion and cooling cycles of the device, the high hydrodynamic forces produced during the ink ejection cycle, and the corrosive effect of the ink.
The present invention is directed to a method of attaching components of a printing device, such as the orifice plate and print head base of an ink-jet pen, without the use of conventional thermal-cure adhesives. Accordingly, the above mentioned problems associated with the thermal-cure adhesive attachment technique are avoided.
One aspect of the invention includes a method of manufacture that can be characterized as thermo-compressive welding and includes the steps of applying a first layer of conductive material to a first component (for example, an orifice plate) of an ink-jet print head or pen. A second layer of conductive material is applied to a second component (such as the base of the print head), and an electric current is applied through the first and second conductive layers by an amount sufficient to heat those layers to melt, or initiate chemical reaction between, the portions of the first and second components that are adjacent to the first and second conductive layers. The heated portions of the first and second components are pressed together so that the heated portions of the components intermix and join.
Another aspect of the invention includes a printing device constructed in accordance with the method of the present invention.